(CNN) -- The parents of a Pakistani man charged in Chile with illegally possessing explosives say his case is the result of a misunderstanding.

A judge released Mohammed Saif-ur-Rehman Khan, 28, from jail Saturday but ruled he must check in weekly with authorities while prosecutors build their case.

Khan was arrested last week after setting off detectors that check for explosives at the U.S. Embassy in Santiago.

In an interview Saturday, his parents said he was innocent.

"I'm full of grief and sorrow. I don't know why this happened. It is a strange story," his mother, Parvin Mahmood, told CNN.

Mahmood and her husband, Mahmood Ahmad Khan, said they were shocked when they heard detectors at the U.S. Embassy had found traces of explosives on their son's clothes Monday.

A framed portrait in their home shows him smiling and wearing a Tommy Hilfiger T-shirt. A large fashion poster featuring a blond model still hangs on the wall of his bedroom.

"This is a misunderstanding. Six months before, he was here. All the time he was very against fundamentalists. He played guitar and everything," his father, Mahmood Ahmad Khan, said.

In a closed hearing Saturday in Santiago, Chile, officials said detectors found residue of the explosive materials TNT and tetryl on Khan's cell phone and documents when he arrived at the U.S. Embassy in Chile's capital . Later, officials said, a search of Khan's apartment found the same particles on clothing, a suitcase and a laptop bag.

He was detained for five days under Chile's antiterrorism law. Prosecutors asked a judge to keep Khan in jail during their investigation.

But Carolina Araya, the judge of the 4th Court of Santiago, ruled that applicable laws, the suspect's lack of a prior criminal record and the lack of evidence suggesting flight risk "do not support the need to deprive the accused of his freedom," according to a summary posted on the Chilean judiciary's website.

"I am innocent," Khan told reporters in English through an open window of the vehicle in which he was being transported by authorities last week. "I have nothing to do with any chemicals."

Embassy officials had asked Khan to come in for a routine consular issue, State Department spokesman P.J. Crowley said.

Crowley declined to elaborate last week on why the man had been asked to go to the embassy. He said U.S. officials would collaborate with Chilean authorities and conduct their own investigation.

A senior U.S. official told CNN the man was on a watch list and had been tracked for some time because he was believed to be involved with an extremist group based in the Western Hemisphere. The official declined to identify the group.

"As far as we can tell, the origin of the activities which brought him to our attention were more of a local or regional nature than international," the official said. "He came to Chile on a student visa and while there he associated himself with a group that we have some knowledge of that was espousing extremist anti-Western views."

The official said the association was enough to call him to the U.S. embassy in Chile to revoke his visa.

Interior Minister Rodrigo Hinzpeter told CNN Chile that Khan had entered the country January 15 on a tourist visa and was doing an internship in tourism at a Chilean hotel.

Chilean authorities searched his apartment in a student housing district in central Santiago, CNN Chile reported. Video showed officials in white hazmat suits carrying items out of an apartment.

The incident occurred a week after Faisal Shahzad -- a Pakistani-born naturalized U.S. citizen -- was arrested in connection with a failed car bombing in New York's Times Square.